The invention relates generally to wide field of view optical systems and more particularly to providing a foveated imaging optical system using a simplified optical system with a spatial light modulator.
The human eye has a wide field of view (FOV) but the spatial resolution decreases as a function of the angular distance from the direction of gaze or point of fixation. The retina has a high concentration of cone photoreceptors within a few degrees of the point of gaze. This central area of high cone density is called the fovea. Cone density and consequently spatial resolution fall off rapidly with increasing field angle measured from the point of fixation. Resolution drops 50% at 2.5 degrees off the point of gaze and by a factor of ten at 20 degrees .
This phenomenon has been exploited in a number of ways to reduce the bandwidth required to transmit digital images. For example, a spatially variant filter or a software algorithm might be applied to an otherwise high-resolution image that would maintain high fidelity around a fixed point in the field-of-view, the region of interest, while reducing spatial resolution over the rest of the image. This foveated imaging mimics the human eye and reduces the bandwidth needed to transmit the useful image. Eye tracking apparatus or a computer mouse might be used at the receiving end to move the region of interest over the image. The spatially variant filter would then track this xe2x80x9ceyexe2x80x9d movement, keeping the high-resolution portion of the image at the point of gaze., (Geisler, W. S. and Perry, J. S. (1998), xe2x80x9cA real-time foveated multi-resolution system for low-bandwidth video communication,xe2x80x9d In B. Rogowitz and T. Pappas (Eds.), Human Vision and Electronic Imaging, SPIE Proceedings, 3299, 294-305.)
While these foveated-imaging systems reduce the required bandwidth of digitally transmitted images, they still require high-quality and potentially complex optical imaging systems to produce the initial high-resolution images, i.e., near diffraction limited quality over the entire image for wide FOV, low f-number systems. There is a need for a relatively simple and inexpensive optical imaging system with a wide FOV and low f-number that would create a foveated image at the transmitting end of a video transmission, i.e., an optical imaging system that would yield high resolution only for that portion of the image corresponding to the region of interest at the receiving end. Degraded resolution would be acceptable away from the point of fixation or interest.
A preferred embodiment of the invention uses a relatively simple and potentially inexpensive optical system with a spatial light modulator (SLM) located at or near a pupil plane to produce a foveated image. This system increases the useable FOV of a wide-angle, low f-number optical imaging system. The SLM is programmed to correct aberrations and, therefore, provide maximum resolution at a particular point of interest within the FOV of the system. Degraded resolution occurs away from the point of interest, mimicking the variable spatial resolution of the human eye. This enables a simple and inexpensive optical imaging system to be employed for a fixed, wide-angle, low f-number surveillance system, for example, while taking advantage of the reduced bandwidth necessary to transmit the image to a remote site. The point of interest can be remotely varied using a preset scan pattern, an eye tracking apparatus, track ball, or other device. The system can also be used for tracking the movement of an object of interest within the FOV.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawing, illustrating by way of example the principles of the invention.